This invention relates to electronic data processing systems, and in particular to memory addressing subsystems having a need for relatively large amounts of addressable random access memory (RAM). This invention has particular utility in providing enhanced, flexible RAM expansion capacities by providing the equivalent of next generation monolithic RAM devices packaged in modules of standardized form such as Single-In-Line-Memory-Modules (SIMMs) at a much earlier point in time (typically three years) using current generation RAM devices packaged in high density, multichip memory modules such as Stakpak.TM. which are then packaged in the same standardized form modules. This achievement is done without significantly increasing power requirements (same number of active devices per memory cycle) or requiring system reconfiguration. Furthermore, the interface is designed in such a way that when next generation RAM devices become available, they can be packaged in the same standardized form modules and plugged into the same sockets as the high density multichip modules.